1. Field of the Invention
The present invention relates to a body structure of a motor vehicle, and in particular, to structures of a center pillar and a floor of a motor vehicle.
2. Prior Art
Generally, as shown in FIG. 14, a center pillar "a" is constituted by a center pillar inner panel and a center pillar outer panel, which form together a closed cross section thereof. Further, the center pillar "a" is connected at the lower end thereof with a side sill "b" having a hollow section extending longitudinally and is connected at the upper end thereof with a roof side rail having a closed cross section extending longitudinally. Further, an inner side of the side sill "b" is fixed to a floor "c", and a cross member "d" is provided transversely on the floor "c". The end portion of cross member "d" is connected at the connecting portion of the center pillar "a" with the inner side of the side sill "b".
As an example of an improvement of the center pillar constituted above, Japanese Utility Application No. Jitsu-Kai-Sho 61-7473 discloses, as shown with a broken line in FIG. 14, a technique where the end portion of the cross member "d" is connected through a bracket "d'" with the lower end of the center pillar "a" so as to transfer a load applied to the lower portion of the center pillar "a" to the cross member "d" with high rigidity, for the purpose of enhancing the entire rigidity of the vehicle body.
Further, generally, since the center pillar is located adjacent to an operator or a passenger on the front seat of the vehicle, the manner of deformation of the center pillar toward the inside of the vehicle has a great influence on the amount of injury inflicted on the passenger or operator in the event of a side impact. That is, in most vehicles, the center pillar is constituted by a thick part (having a large cross section) at the lower portion below the window line and a thin part (having a small cross section) at the upper portion above the window line, and the cross section of the center pillar largely changes at the border of the lower and upper portions. Because of this construction, it is possible that the center pillar will bend near that border at the middle of the center pillar when the vehicle is subjected to a side impact. In this case, since the bending occurs at the middle portion of the center pillar, as shown in FIG. 16, a large amount of deformation of the center pillar is caused toward the inside of the vehicle, and as a result, there is a likelihood that the passenger or operator would be seriously injured.
In order to avoid this disadvantage, the assignee of the present invention has proposed an improved center pillar in Japanese Laid Open Patent Publication No. 6-72787. In this improved center pillar, there is intentionally provided a strength discontinuity portion 1a, i.e., a portion easy to bend when a side force is applied thereto, at the lower part of the center pillar as shown in FIG. 15. At the initial stage of side impact, only the strength discontinuity portion (referred to as "a yieldable portion" hereinafter) 1a bends, and the upper portion of the center pillar does not. As a result, the center pillar is deformed toward the inside of the vehicle with the original configuration substantially retained, and the amount of deformation is relatively small, whereby an impact on the passenger can be minimized.
In order that the center pillar according to this utility model application bends at the yieldable portion 1a and is deformed as intended in the event of a side impact, the upper and lower ends of the center pillar, specifically the lower end portion thereof, must withstand an impact load. Therefore, since the aforementioned reinforcement member bracket "d" is just connected with the lower end of the center pillar, it is insufficient to positively support the impact load.
Further, according to the prior art illustrated in FIG. 14, when a side impact is applied, first the impact load is transferred to a center tunnel through the cross member d and the floor c. Since the center tunnel is relatively weak against a transverse force, although it is strong against a longitudinal force, the center tunnel is collapsed before the center pillar and the side sill are collapsed. That is to say, the whole member, including the center pillar and the side sill, is deformed toward the inside of the vehicle, and the impact energy can not be absorbed effectively.